Introduce the clean_retired_packages toddler
    
    This toddler ensures retired packages are properly orphaned and
    have no (co)maintainers set to properly reflect in the dist-git's UI
    that these packages are not maintained by anyone.
    
    Fixes https://pagure.io/fedora-infrastructure/issue/8600
    (which contains all the references to how we came to do this,
    including link to the FESCo ticket approving this).
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>